This invention relates to a generically well known process variously called xe2x80x9cphosphatingxe2x80x9d, xe2x80x9cphosphatizingxe2x80x9d, or xe2x80x9cphosphate conversion coatingxe2x80x9d in which a metallic substrate is coated with an adherent coating containing phosphate anions and metal cations, at least some of these metal cations being those corresponding to one or more metallic constituent(s) of the substrate. If the phosphating composition also contains divalent cations that can form only sparingly water-soluble phosphates, the conversion coating formed also normally includes some of these divalent cations from the phosphating composition.
Normally, a phosphate coating is formed by chemical reaction between the metal substrate and an aqueous liquid variously called a xe2x80x9cphosphatingxe2x80x9d or xe2x80x9cphosphatizingxe2x80x9d composition, solution, bath, or a like term; in some instances, the formation of the coating may be aided by, or even completely dependent on, application of an electric current. If the phosphating composition is in contact with the substrate for at least about five seconds at a temperature not more than 70xc2x0 C. and any liquid phosphating composition remaining in contact with the conversion coating thus formed is rinsed off before the substrate treated with it is dried, the phosphate coating formed generally is microcrystalline, particularly if the substrate and/or the phosphating composition contains substantial amounts of iron and/or zinc. If the phosphating composition is applied to the substrate and dried in place without rinsing, the coating formed is usually predominantly amorphous.
The presence of a phosphate coating on a metal substrate normally serves one or both of two major functions: (1) increasing the corrosion resistance of the substrate by comparison with an otherwise identical metal substrate that has no such conversion coating, an increase that may be measured either with or without a subsequent paint or similar protective coating and (2) serving as a strongly adherent xe2x80x9ccarrierxe2x80x9d for an externally applied lubricant material that facilitates mechanical cold working.
A major object of this invention is to achieve an additional benefit from a phosphate conversion coating in an operation of this latter type. The specific benefit achieved is a reduction in the coefficient of sliding friction of the conversion coated and lubricated surface, compared to the surface achieved with a conventional phosphate conversion coating that is lubricated in the same manner. Such a reduction in surface friction facilitates relatively minor mechanical formability such as is needed for stamping, bending into corners, and the like, particularly for such operations that are involved in the manufacture of automobile body parts, appliances, metal furniture, and the like from suitably prepared metal sheets and/or coils, normally without substantially reducing the thickness of the sheet or coil material used over most of its area. In some instances, this reduction of the coefficient of the coated substrate preferably is achieved without sacrificing the corrosion protective qualities of a conventional phosphate coating applied for this purpose. In many instances, however, this is a relatively minor consideration, because the substrates initially coated with a phosphate-containing coating to facilitate the mechanical working are coated with another corrosion protective conversion coating, after they have been put into their final intended shape. Other more detailed objects of the invention will become apparent from the description below.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word xe2x80x9caboutxe2x80x9d in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, xe2x80x9cparts ofxe2x80x9d, and ratio values are by weight or mass; the term xe2x80x9cpolymerxe2x80x9d includes xe2x80x9coligomerxe2x80x9d, xe2x80x9ccopolymerxe2x80x9d, xe2x80x9cterpolymerxe2x80x9d and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word xe2x80x9cmolexe2x80x9d means xe2x80x9cgram molexe2x80x9d, and the word itself and all of its grammatical variations may be used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; an abbreviation once defined may be used thereafter with either exactly the same meaning or a grammatically varied meaning as indicated by the context and is to be understood as having the same meaning, mutatis mutandis, as when first defined; and the terms xe2x80x9csolutionxe2x80x9d, xe2x80x9csolublexe2x80x9d, xe2x80x9chomogeneousxe2x80x9d, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained within the range of 18-25xc2x0 C.
It has been found that the above stated object of the invention can be achieved by combining with a conventional phosphating composition an additive selected from the group consisting of (i) water-soluble and water-dispersible phosphate esters and (ii) natural and synthetic waxes that are water-dispersible and are not phosphate esters. Specific embodiments of the invention include phosphating compositions containing one or more of these additives, processes for forming a phosphate conversion coating from such a phosphating composition and a metal substrate, and articles of manufacture including surfaces treated by such a process and/or surfaces having a phosphate conversion coating that includes one or more of these additives.